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United States Patent |
6,048,649
|
Burke
,   et al.
|
April 11, 2000
|
Programmed defect mask with defects smaller than 0.1 .mu.m
Abstract
A method is provided for making sublithographic structures, such as
programmed defect masks. The method comprises the steps of forming a layer
of base material on a substrate, the base material being selectively
definable from the substrate, forming a layer of photosensitive material
over the layer of material, selectively exposing a plurality of image
segments in the photosensitive material in which segments are offset from
each other by a sub-lithographic dimension in a first direction and a
different dimension in a second direction and a sub-plurality of the
segments pass over the layer of base material, and developing the
photosensitive material to expose the layer within the sub-plurality of
segments. Also provided is the resulting programmed defect mask with
defects under 0.1 .mu.m in size.
Inventors:
|
Burke; Ann Rand (South Burlington, VT);
Rigaill; Denis Marc (South Burlington, VT);
Smolinski; Jacek Grzegorz (Jericho, VT)
|
Assignee:
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International Business Machines Corporation (Armonk, NY)
|
Appl. No.:
|
070625 |
Filed:
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April 30, 1998 |
Current U.S. Class: |
430/5; 430/324 |
Intern'l Class: |
G03F 009/00 |
Field of Search: |
430/5,22,322,324,394
|
References Cited
U.S. Patent Documents
4762805 | Aug., 1988 | Cheung et al. | 437/63.
|
5087537 | Feb., 1992 | Conway et al. | 430/15.
|
5260175 | Nov., 1993 | Kowanz et al. | 430/326.
|
5585211 | Dec., 1996 | Firstein et al. | 430/30.
|
5804088 | Sep., 1998 | McKee | 430/313.
|
Foreign Patent Documents |
61-061417 | Mar., 1986 | JP.
| |
Primary Examiner: Rosasco; S.
Attorney, Agent or Firm: Walter, Jr.; Howard J.
Claims
What is claimed is:
1. A method of making sub-lithographic structures comprising the steps of:
forming a layer of base material on a substrate, said base material being
selectively definable from said substrate, said base material including at
least one edge;
forming a layer of photosensitive material over said layer of base
material;
sequentially exposing a plurality of latent image segments in said
photosensitive material in which segments are offset from each other by a
sub-lithographic dimension in a first direction and a different dimension
in a second direction and a sub-plurality of said segments pass over said
at least one edge of said layer of base material; and
developing said photosensitive material to expose said layer of base
material within said sub-plurality of segments.
2. The method of claim 1 wherein said layer of base material includes an
edge over which said plurality of image segments passes.
3. The method of claim 2 wherein the step of developing is followed by
etching said layer exposed in said developing step.
4. The method of claim 3 wherein said different dimension is substantially
greater than said sub-lithographic dimension.
5. The method of claim 4 wherein said layer of base material is optically
opaque and said substrate is optically transparent.
6. The method of claim 1 wherein the base material comprises chrome.
7. The method of claim 1 wherein the photosensitive material comprises PBS
resist.
8. The method of claim 7 wherein the step of developing further comprises
developing the PBS resist using methyl isoamyl ketone/methyl n-propyl
ketone.
9. The method of claim 1 wherein the step of selectively exposing further
comprises selectively exposing the plurality of image segments using an
e-beam tool or an optical tool.
10. A method of making a programmed defect mask, comprising:
forming a base material on a substrate;
applying a first layer of photosensitive material to the base material;
exposing a first large base geometry image pattern on the first layer of
photosensitive material to form a first level mask;
processing the first level mask;
adding a second layer of photosensitive material on top of the first level
mask;
exposing a second pattern on the second layer of photosensitive material to
form a second level mask; and
processing the second level mask.
11. The method of claim 10, wherein the step of processing the first level
mask further comprises:
developing, etching, and stripping the first level mask.
12. The method of claim 10, wherein the step of processing the second level
mask further comprises:
developing, etching, and stripping the second level mask.
13. The method of claim 10, wherein the base material is optically opaque.
14. The method of claim 10, wherein the substrate is optically transparent.
15. The method of claim 10, wherein the base material comprises chrome.
16. The method of claim 10, wherein the first layer of photosensitive
material comprises PBS resist or an optical resist.
17. The method of claim 10, wherein the second layer of photosensitive
material comprises PBS resist or an optical resist.
18. The method of claim 10, wherein the step of exposing the first large
base geometry image pattern further comprises selectively exposing the
first large base geometry image pattern using an e-beam tool or an optical
tool.
19. The method of claim 10, wherein the step of exposing the second pattern
further comprises selectively exposing the second pattern using an e-beam
tool or an optical tool.
20. The method of claim 10, wherein the first large base geometry image
pattern comprises image segments 0.5 .mu.m or smaller in size.
21. The method of claim 10, wherein the step of exposing the second pattern
further comprises using the smallest available increment of stepper motion
available on the exposure tool exposing said second layer of photoresist
material.
22. The method of claim 10, wherein the processing of the first level mask
uses different techniques from the processing of the second level mask.
23. The method of claim 10, further comprising determining defects on the
mask after the step of processing the second level mask.
24. The method of claim 10, wherein the steps of adding the second layer,
exposing the second pattern, and processing the second level mask are
repeated as many times as desired.
25. A programmed defect mask with defects smaller than 0.1 .mu.m in size.
26. The programmed defect mask of claim 25, further comprising:
a substrate;
a base material on top of the substrate;
a first layer of photosensitive material on top of the substrate;
a first level mask of exposed and processed first large scale geometry
images pattern on the first layer of photosensitive material;
a second layer of photosensitive material on top of the first level mask;
and
a second level mask of exposed and processed second smaller images
patterned on the second layer of photosensitive material.
27. The programmed defect mask of claim 25, wherein the base material is
optically opaque.
28. The programmed defect mask of claim 25, wherein the substrate is
optically transparent.
29. The programmed defect mask of claim 25, wherein the base material
comprises chrome.
30. The programmed defect mask of claim 25, wherein the first layer of
photosensitive material comprises PBS resist or optical resist.
31. The programmed defect mask of claim 25, wherein the second layer of
photosensitive material comprises PBS resist or optical resist.
Description
TECHNICAL FIELD OF THE INVENTION
The invention relates to programmed defect masks used to characterize mask
defect inspection systems.
BACKGROUND OF THE INVENTION
As improvements are made in wafer exposure systems, it has become
increasingly important for chip manufacturers and chip testers to have the
ability to identify smaller and smaller defects. Mask defect inspection
systems are used to identify defects in masks. Programmed defects are
sub-lithographic structures that are used to characterize the mask defect
inspection system to ensure the defect inspection system is running
smoothly. A programmed defect mask is a mask with programmed (i.e., known)
defects. Programmed defect masks with defects above 0.1 .mu.m in size
presently exist.
One such programmed defect mask is made by Dupont PhotoMask, and is called
the Verimask. The Verimask is built with standard lithography techniques
using numerical control ("NC") data for the defect written on the mask
with the images ground rules ("G/R") at the same time. As improvements are
made in wafer exposure systems the minimum defect allowed is decreasing
and mask inspection systems will be required to find smaller defects. A
need exists to create a programmed defect mask with defects under 0.1
.mu.m in size.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a programmed defect mask
with defects of under 0.1 .mu.m in size.
Another object of the present invention is to provide a method for building
a programmed defect mask with defects under 0.1 .mu.m in size.
Another object of the present invention is to provide a method for building
a programmed defect mask that has a higher level of reliability than the
present state of the art.
Accordingly, a method is provided for making sublithographic structures,
such as programmed defect masks. The method comprises the steps of forming
a layer of base material on a substrate, the base material being
selectively definable from the substrate, forming a layer of
photosensitive material over the layer of material, selectively exposing a
plurality of image segments in the photosensitive material in which
segments are offset from each other by a sub-lithographic dimension in a
first direction and a different dimension in a second direction and a
sub-plurality of the segments pass over the layer of base material, and
developing the photosensitive material to expose the layer within the
sub-plurality of segments. Also provided is the resulting programmed
defect mask with defects under 0.1 .mu.m in size.
An advantage of the present invention is that it provides a programmed
defect mask with defects of under 0.1 .mu.m in size. The present invention
also offers a high degree of repeatability. The present invention also
provides a method for building a programmed defect mask with defects of
under 0.1 .mu.m in size. The method of the present invention is highly
reliable, since no matter what the overlay error is between the two levels
of images used in the method, at some point, the second level images have
to hit the first level images and have to hit the first level images in
very small increments.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows the component materials used in the present invention to make
a programmed defect mask using two levels of images.
FIG. 2 shows a programmed defect mask using two levels of images in
accordance with the present invention.
FIG. 3 shows the resulting defects in the programmed defect mask
manufactured in accordance with the present invention.
FIG. 4 is a flow chart of the method of the present invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
The invention is directed to a sub-lithographic structure called a
programmed defect mask and the method of making the mask. The programmed
defect mask of the present invention has defects under 0.1 .mu.m in size.
The programmed defect mask thus is suitable to characterize a mask defect
inspection system to ensure the inspection system is operating correctly
and does identify defects of under 0.1 .mu.m in size.
FIG. 1 shows the component materials used in the present invention to make
a programmed defect mask using two levels of images. Substrate 4 is likely
to be composed of a quartz, also called a quartz plate. Other suitable
materials for substrate 4 include, but are not limited to, attenuated
masks and X-ray masks. The substrate 4 may be optically transparent. On
top of substrate 4 is base material 6. In the preferred embodiment of the
invention, base material 6 is chrome. Other suitable materials for base
material 6 include, but are not limited to, attenuated PSM materials (such
as those sold under the trade names Iline and DUV), X-ray absorbers, and
any other material used for pattern imaging. Base material 6 is
selectively definable from substrate 4. The base material 6 may be
optically opaque. Photosensitive material 8 lies on top of base material
6. Examples of photosensitive material 8 include PBS resist or other kind
of resist and, in general, any kind of exposure sensitive material that
can be selectively removed. In some cases, both level 6 and 8 can be
multiple level structures.
FIG. 2 shows a programmed defect mask using two levels of images in
accordance with the present invention. FIG. 2 shows first large base
geometry images (ground rules) 10. The first large base geometry images 10
are formed by selectively exposing areas of photosensitive material 8
(shown in FIG. 1). The first large base geometry images 10 are of
approximately the size of 0.5 .mu.m or smaller if lithography capability
allows formation of such images. The first large base geometry images 10
may be of various types. Typically the first large base geometry images 10
repeat across the mask and create at least one edge over which the second
smaller images 12 must pass.
Standard lithography techniques are used to write the first large base
geometry images 10. The standard lithography techniques generally may
include x-ray, ion, e-beam or optical methods. These methods are known in
the industry by various trade names of their tools, including MEBES
(e-beam tool), Alta and Core (both optical tools), among others. An e-beam
tool generally requires a PBS or other e-beam sensitive resist. An optical
tool generally requires an "895i" resist, which refers to optical resist.
The standard lithography techniques may utilize dry/wet processing.
As seen in FIG. 2, a set of second smaller images 12 of various sizes,
dose, and shapes is moved in a least lithography stepper motion printing
on a second resist. This step size capability varies from exposure tool to
exposure tool. The least lithography stepper motion is the smallest
available increment for a given exposure tool with which an image can be
placed on the second resist. The result of this is that the defect is
incrementally imaged on the first large base geometry image 10 in
horizontal positions across the mask for defect sizes. In the single level
processes of the prior art there is no capacity to adjust for size, dose,
shape or process. The defect types also can be programmed on vertical
positions using the same second layer technique. The mask is processed for
the second smaller images 12 such as by etching after the development of
the second smaller images. Different process parameters are permitted for
the second smaller images 12 than those used for the first large base
geometry images ground rules 10. By varying the process it is possible to
resolve the smaller defects. The second exposure process builds the defect
images into the first exposures from the first large base geometry images
10 and the processed mask. The goal in exposing the second smaller images
12 is to produce the smallest possible defects within the first large base
geometry images 10.
The first large base geometry images 12 and the second smaller images 10
thus form a plurality of image segments. The plurality of image segments
of the first large base geometry images 10 and the second smaller images
12 thus are offset from each other by a first sub-lithographic dimension
16 in a first direction and a second and different sub-lithographic
dimension 14 in a second direction.
One can determine the lower limit of the size of the defects to be
detected, by adjusting the separation 14 between the second smaller images
12. Also relevant to the lower limit of the size of the defects to be
detected is the placement least significant bit (placement LSB) 16 of the
exposure tool used. The placement LSB is the increment with which
placement of the exposure beam is controlled. The placement LSB 16
typically is in the range of 5 .mu.m to 6.25 .mu.m but could be less if
permitted by a given lithography tool.
FIG. 3 shows the result of the two level of images process of building a
programmed defect mask performed in accordance with the present invention.
FIG. 3 shows a defect 20 that is of a size between 0 and the placement
LSB. The defects are arranged in a horizontal line, with each successive
defect incrementally larger than the prior defect by the width of the
placement LSB. For example, defect 22 is the size of defect 20 plus the
placement LSB. In general, defect N (not labeled) is of a size that equals
the size of defect N-1 plus the placement LSB, where the placement LSB is
the size of the smallest placement step exposure tool used.
An alternative embodiment of the invention would result in a vertical
arrangement of the progressively larger defects rather than a horizontal
arrangement as shown in FIG. 3.
FIG. 4 summarizes the steps of the method of the present invention. In step
30, a layer of base material is formed on a substrate. A layer of
photosensitive material is applied to the base material in step 32. In
step 34, a first large base geometry image is exposed in a pattern on the
photosensitive material. Standard mask making techniques are used in step
34, as described above. In step 36, the mask is developed, etched and
stripped in a standard process. An example of a standard process is PBS
resist, develop etch, and strip. Other standard processes are known in the
art.
In step 38, a layer of resist, such as PBS or 895i resist is applied. This
is used for the second layer processing.
The layer of resist typically is on the range of 500 .mu.m to 2 .mu.m in
thickness.
In step 40, the second level resist is exposed with various doses, shapes
and processes to produce the smallest possible defects within the first
large base geometry image.
In step 42, the second level mask is developed, etched and stripped. PBS
resist, for example, is developed by methyl isoamyl ketone/methyl n-propyl
ketone (MIAK/MNPK). The processes used for the second level mask may be
the same as or different from those used with regard to the processing of
the first large base geometry image. Since only defects are resolved, the
method of the present invention has the advantage of permitting separate
processing of the second level mask, even where the processing used for
the second level mask is drastically different than the processing used
for the first level mask. In some cases, using the same processes for the
second level mask as the first level mask would damage the plate, so it is
important to be able to use a different process for the second level mask.
In step 44, a scanning electron microscope is used to determine defect
locations and sizes. Other detection means are possible.
As shown in FIG. 4, steps 38-42 can be repeated as desired.
Using the method of the present invention it is possible to develop
programmed defect masks with defects under 0.1 .mu.m in size. The
programmed defect masks then are used to characterize mask defect
inspection systems. Moreover, the method of the present invention offers
certainty that defects of all sizes will be resolved.
Although the invention has been described with some particularity, those
skilled in the art will recognize that certain changes and modifications
are possible without departing from the spirit and scope of the invention.
The invention is limited only by the following claims and their
equivalents.
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